AI Tutor
Imagine opening a pair of scissors — snap them nearly shut to make a sharp point, open them like the corner of a book, or stretch them wide open.
Triangles do the exact same thing with their corners, and that gives us three special triangle families.

The Three Angle Types

An angle measures the amount of turn between two lines meeting at a point, measured in degrees (∘^\circ).
A right angle makes a perfect square corner measuring exactly 90∘90^\circ, an acute angle is smaller than 90∘90^\circ, and an obtuse angle is wider than 90∘90^\circ.
How do these three angle shapes decide the name of an entire triangle?

Naming Triangles by Their Angles

An acute triangle has all three angles measuring less than 90∘90^\circ.
A right triangle has exactly one 90∘90^\circ right angle, while an obtuse triangle has exactly one obtuse angle wider than 90∘90^\circ.
Why can't a triangle have two right angles or two obtuse angles?

Why Only One Wide Corner Fits